Darcy signed a two-year extension on Sunday, after committing last season until 2020.
The 20-year-old will remain at the club for the next four years, with only captain Nat Fyfe currently tied down on a longer deal.
The ruckman is looking forward to getting back underway in 2019, and said the decision was an easy one to make.
“As a group we have a great chemistry and we are all really close. It was an easy decision from my end and I am really excited for the future at Freo,” Darcy told fremantlefc.com.au.
“I am close with a lot of the boys so I am loving it here. Ross has been unreal for me during the past two years and I’m enjoying developing with a young group.”
Darcy has played 15 games for the Dockers over the past two seasons, and averages 10.9 disposals, 4.3 tackles, 1.8 marks and 33.7 hitouts per game over his career.